Caltrans describes upcoming work on the Bay Bridge that will shut down the entire span over Labor Day weekend as an “unprecedented construction feat.”

That fits.

Work crews will slice away a 300-foot, 3,300-ton double-deck section of the east span above Yerba Buena Island. And 150 feet above the ground, crews will slide in a 3,600-ton replacement structure that will serve as a detour as work on the new $5.7 billion eastern bridge forges ahead.

That’s a lot of steel being moved at heights that would make many of us dizzy.

“What we are doing is gigantic,” said spokesman Bart Ney of the largest construction feat in Caltrans history. “It’s just massive, a once-in-a-lifetime event in the Bay Area.”

National Geographic will film the event for a documentary. Media helicopters will hover overhead. And hundreds of boats will be floating on chilly Bay Area waters below, the best seats for spectators to catch a glimpse of the work.

This is the third time since 2006 that the bridge will be closed over Labor Day, only the concerns are greater and the closing one day longer.

The span will be shut down from 8 p.m. on Thursday, Sept. 3, until 5 a.m. the following Tuesday — meaning Friday commuters will have to take BART, divert to the San Mateo or Richmond bridges, telecommute or simply take the day off.

A major inconvenience for sure — but the greatest concern is actually the wind.

Moving nearly 7,000 tons of steel at these heights has engineers on a constant weather watch. They hope winds don’t slow work, but they planned an extra closing day just in case.

“We’ll be worrying about the wind all weekend,” Ney said.

The bridge carries about 280,000 vehicles each weekday, but the Labor Day holiday is usually one of the slowest times of the year for traffic, and there are only a few events that weekend to entice people to the area.

The Oakland A’s are hosting Seattle all weekend, the California Bears football team has a home opener Saturday night against Maryland and the Sausalito Arts and Wine Festival is on.

Still, the advice from John Goodwin of the Metropolitan Transportation Commission is: “Don’t drive.”

He thinks travelers will get that message. Caltrans has bombarded drivers from San Diego to Redding with messages on electronic freeway signs warning of the bridge closing. Two years ago, a smattering of problems occurred, mostly on the approach to the Golden Gate Bridge, on Van Ness Avenue and south of Market Street in San Francisco, and on Highway 101 in Marin County.

“People got the message, and they avoided transbay trips or rode BART,” Goodwin said, noting that BART ridership that weekend shattered previous records for Friday, Saturday and Sunday travel. On the Friday of that closure, 389,400 riders flocked to BART — the all-time one-day record.

The California Highway Patrol will have more officers out to keep traffic flowing. San Francisco will deploy officers to monitor and control traffic along Van Ness, Market and around Park Presidio, all marked as corridors to handle traffic that weekend. And the Freeway Service Patrol will boost the number of trucks roaming Bay Area roads to clear accidents and stalls more quickly.

Caltrans is replacing the entire eastern span to make it seismically safe — a project that stems from the collapse of the westbound deck in the 1989 Loma Prieta quake.

Work began seven years ago, after more than a decade of squabbling over what kind of structure should be built. The new bridge will be just north of the current span, which will eventually be demolished.

The temporary span allows Caltrans to move traffic out of the way to demolish the old approach to Yerba Buena Island and place the new approach in the same location.

If work goes well, another challenge remains: Tuesday’s commute.

The day after Labor Day is one of the most heavily traveled on the bridge, and drivers will be facing a new, curvy detour.

As drivers move onto the temporary span — which will remain in place until the new bridge opens in 2013 — they will face a sharp “S” curve with a speed limit of 40 mph, down from 50 mph.

“The ‘S’ curve will screw traffic up,” said John Hamblin, of San Ramon, a frequent Bay Bridge driver. “I think a 40-mph speed limit is as moronic as the current 50 mph one. No one drives that slow when there’s no traffic unless they’re in a funeral procession.”

But Ney cautioned: “In seven decades on this bridge, there’s never been an alignment change like this. People don’t expect an S-turn. They will have to dodge left, go straight and dodge back to the right to get to the tunnel.

“Commuters are the ones I’m concerned about. They do this trip every day and they may not be expecting this change to 40 miles an hour.”

Why: To remove a 300-foot-long double-deck section above Yerba Buena Island and install a new double-deck section as a detour.

Afterward: Speed limit will be 40 mph through curvy detour.

And: Go to BayBridgeinfo.org or www.mtc.ca.gov for more information and a video simulation of the project.

Options: BART will run 24 hours a day, with longer trains. Extra ferries are scheduled for Alameda-Harbor Bay on Friday and Alameda-Oakland on Saturday through Monday, and there will be additional departures on Golden Gate Ferry from Sausalito and Larkspur.

Tips: Call 511 for driving and transit information or go to www.511.org.

Gary Richards has covered traffic and transportation in the Bay Area as Mr. Roadshow since 1992. Prior to that he was an assistant sports editor at the paper from 1984-1987. He started his journalism career as a sports editor in Iowa in 1975.

Otto Warmbier was arrested in January 2016 at the end of a brief tourist visit to North Korea. He had been medically evacuated and was being treated at the University of Cincinnati Medical Center when he died at age 22.